U.S. patent number 5,564,896 [Application Number 08/510,777] was granted by the patent office on 1996-10-15 for method and apparatus for shaft sealing and for cooling on the exhaust-gas side of an axial-flow gas turbine.
This patent grant is currently assigned to ABB Management AG. Invention is credited to Alexander Beeck, Eduard Bruhwiler.
United States Patent |
5,564,896 |
Beeck , et al. |
October 15, 1996 |
Method and apparatus for shaft sealing and for cooling on the
exhaust-gas side of an axial-flow gas turbine
Abstract
In a method and an apparatus for shaft sealing and for cooling
on the exhaust-gas side of a thermal turbomachine, in particular an
axial-flow gas turbine, in which the outlet-side bearing
arrangement of the turbine rotor is made inside the exhaust-gas
casing construction, and labyrinth seals and a gland are used for
the sealing, barrier air having a higher pressure than the pressure
of the exhaust gas in the exhaust-gas duct being directed for the
shaft sealing into the gland and then into the exhaust-gas duct,
and the rotor cooling air being extracted from a compressor stage
and being fed via a pipeline through the exhaust-gas-side shaft end
into the rotor, a portion of the rotor cooling-air leakage is
diverted after some of the labyrinth seals and is used as barrier
air. In addition, ambient air is introduced as cooling air into the
bearing space, is uniformly distributed at the periphery via the
gland separately from the barrier air, is partly used through
cooling ducts for specifically cooling the supporting structure and
is transported to the outside through passages in the exhaust-gas
diffuser.
Inventors: |
Beeck; Alexander (Endingen,
CH), Bruhwiler; Eduard (Turgi, CH) |
Assignee: |
ABB Management AG (Baden,
CH)
|
Family
ID: |
6529844 |
Appl.
No.: |
08/510,777 |
Filed: |
August 3, 1995 |
Foreign Application Priority Data
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Oct 1, 1994 [DE] |
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44 35 322.7 |
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Current U.S.
Class: |
415/175;
415/112 |
Current CPC
Class: |
F01D
5/08 (20130101); F01D 11/04 (20130101) |
Current International
Class: |
F01D
11/00 (20060101); F01D 5/02 (20060101); F01D
5/08 (20060101); F01D 11/04 (20060101); F01D
025/18 () |
Field of
Search: |
;415/111,112,175,176 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1258330 |
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Mar 1961 |
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FR |
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1069428 |
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Jun 1958 |
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DE |
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2008209 |
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Sep 1970 |
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DE |
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2043480 |
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Apr 1971 |
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DE |
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2408839 |
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Aug 1974 |
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DE |
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3447740 |
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Jul 1985 |
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DE |
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1041712 |
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Sep 1983 |
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SU |
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Primary Examiner: Look; Edward K.
Assistant Examiner: Sgantzos; Mark
Attorney, Agent or Firm: Burns, Doane, Swecker &
Mathis
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. A method of shaft sealing and of cooling on the exhaust-gas side
of a thermal turbomachine, the turbo-machine including an
outlet-side bearing arrangement of a turbine rotor, an exhaust-gas
casing construction having an exhaust gas diffuser defining an
exhaust-gas duct through which exhaust gas flows and inside of
which the bearing arrangement is disposed, the bearing arrangement
having a bearing space in flow communication with the exhaust-gas
duct, through a plurality of labyrinth seals and one or more glands
for preventing exhaust gas from entering the bearing space,
comprising the steps of:
directing barrier air having a higher pressure than a pressure of
exhaust gas in the exhaust-gas duct into the one or more glands and
then into the exhaust-gas duct to seal the bearing space;
extracting rotor cooling air from a compressor stage;
feeding the rotor cooling air, via a pipeline, into the rotor;
diverting a portion of the rotor cooling air, the diverted portion
of cooling air being directed by the plurality of the labyrinth
seals such that at least a first portion of the diverted portion of
cooling air flows through a barrier gas pipeline for use as the
barrier air and a second portion of the diverted portion of cooling
air flows into the bearing space;
introducing and uniformly distributing ambient air into a periphery
of the bearing space via the one or more glands separately from the
barrier air; and
transporting the ambient air to an outside of the turbomachine
through passages in the exhaust-gas diffuser.
2. The method as claimed in claim 1, wherein the labyrinth seals
include first and second labyrinth seals, the first and second
labyrinth sealing include first and second groups of sealing
strips, respectively, the first and second groups of sealing strip
being disposed in first and second passage portions, respectively,
and defining first and second gap sizes therewith, respectively,
the method comprising the step of changing a quantity and a
pressure of the barrier air by changing at least one of a number
sealing strips of the first and second groups of sealing strips,
and the first and second gap sizes defined by the first and second
sealing strips and the first and second passages, respectively.
3. The method as claimed in claim 1, wherein the one or more glands
include an annular cooling-air space into which the ambient air is
introduced and from which the ambient air is uniformly distributed
for cooling supporting ribs of the turbomachine.
4. A thermal turbomachine, the turbo-machine including
an outlet-side bearing arrangement of a turbine rotor;
an exhaust-gas casing construction having an exhaust gas diffuser
defining an exhaust-gas duct through which exhaust gas flows, the
bearing arrangement being disposed inside of the exhaust gas
duct;
a bearing space of the bearing arrangement, the bearing space
including a top part and a bottom part, the top part being
subdivided into first and second parts by a hood and the bottom
part being subdivided into first and second parts by an oil drip
plate;
a pipeline for feeding rotor cooling air into the rotor;
a gap in the pipeline, a portion of the rotor cooling air being
diverted into the gap and into a first passageway, the first
passageway having a first labyrinth seal, the first passageway
being in flow communication with a barrier gas pipeline, the
barrier gas pipeline leading to a first annular portion of a gland,
and with a second passageway, the second passageway having a second
labyrinth seal and being in flow communication with the bearing
space;
the gland having the first annular portion and a second annular
portion, the first annular portion being in flow communication with
the exhaust gas duct, the second annular portion being in flow
communication with the first and second parts of the top and the
bottom parts of the bearing space;
an ambient cooling air pipeline extending through the bearing space
to the second annular space.
5. The apparatus as claimed in claim 4, wherein the exhaust gas
casing includes an inner part including a supporting structure and
along supporting ribs of the exhaust gas casing, the apparatus
further comprising cooling ducts arranged between the supporting
structure and the insulation, the cooling ducts being connected, at
turbine-side inlet parts thereof, via bores to the second annular
space of the gland and, at outlet parts thereof, to the bearing
space.
6. The apparatus as claimed in claim 5, wherein the supporting ribs
each include a foot, the cooling ducts being arranged on opposite
sides of the foot of each of the supporting ribs.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and an apparatus for shaft
sealing and for cooling on the exhaust-gas side of a thermal
turbomachine, in particular an axial-flow gas turbine.
2. Discussion of Background
It is known that thermal turbomachines, in particular axial-flow
gas turbines, essentially consist of the bladed rotor and the blade
carrier, which is equipped with guide blades and hung in the
turbine casing. Adjoining the turbine casing is the exhaust-gas
casing, which in modern machines is flanged to the turbine casing
and essentially consists of a hub-side annular inner part and an
annular outer part which define the exhaust-gas diffuser. The inner
part and the outer part are connected to one another by a plurality
of radial flow ribs arranged uniformly over the periphery. The
outlet-side bearing arrangement of the turbine rotor is disposed in
the hollow space inside the inner part, that is, inside the
diffuser construction itself.
Shaft seals (labyrinth seals, gland) are present for the noncontact
sealing of the leadthroughs of the rotor through the exhaust-gas
casing and for reducing the leakage to a suitable proportion.
In order to prevent hot exhaust gases from being able to penetrate
into the bearing space, compressor air has hitherto been extracted
from a certain stage, directed via a separate line to the
exhaust-gas casing and fed as barrier air directly into the gland
on the exhaust-gas side. A portion of the air escapes through the
seal into the bearing space, the rest flows along the shaft disk
into the hot-gas duct.
If a compressor having one or more variable guide blades is used in
a gas turbine and if these guide blades are closed by a certain
amount in the partial-load range, this results in a lower pressure
at the extraction point of the barrier air relative to the pressure
during full-load operation. Therefore, so that there is sufficient
barrier-air pressure in each operating state, either air has to be
extracted at a high stage in which there is always sufficient
pressure or a changeover has to be made between different
stages.
The extraction of the air at a high stage has the disadvantage that
highly compressed air is "consumed" at full load without power
output, which has an adverse effect on the efficiency of the gas
turbine. On the other hand, if a changeover is made between
different stages, more extraction points at the compressor and
changeover valves are necessary, so that the costs increase.
If cooling air has to be introduced through the exhaust-gas-side
shaft end into the rotor, the rotor cooling air is also extracted
from a certain compressor stage in addition to the barrier air and
is fed via a special pipeline into the rotor. The transition of
pipeline/rotor is here sealed off with labyrinth seals. The
labyrinth leakage air passes into the surroundings of the bearing
and leads to heating-up of the bearing space. This is undesirable,
since the bearing temperature is limited because of the devices
present, the bearing oil and the possibility of an inspection.
Apart from the leakage of barrier air and rotor cooling air, the
bearing space is also heated up by the heat flow from the
exhaust-gas stream through the insulation or the supporting
structure. In most machines, the bearing space is cooled by natural
convection. It is also known to cool the bearing space by cooling
air which enters through openings in the exhaust-gas diffuser and
leaves through the gap between lining and rib of the exhaust-gas
casing. In this solution, the supporting structure of the
exhaust-gas casing has no uniform temperature at the periphery,
which disadvantageously leads to thermal stressing occurring and/or
to the bearing no longer being concentric.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention, in attempting to avoid
all these disadvantages, is to provide a novel barrier-air and
cooling-air system on the exhaust-gas side in a thermal
turbomachine, in particular an axial-flow gas turbine, which
barrier-air and cooling-air system, with low fabrication and/or
operating costs, prevents the ingress of the exhaust gas into the
bearing space and admits as little air leakage as possible into the
bearing space and with which the bearing-space temperature can be
kept sufficiently low in a relatively simple manner and in which
the supporting structure of the exhaust-gas casing has a uniform
temperature at the periphery.
According to the invention, this is achieved in a method of shaft
sealing between rotating shaft and exhaust-gas casing as well as of
cooling the rotor and the bearing space on the exhaust-gas side of
a thermal turbomachine, in particular an axial-flow gas turbine, in
which the outlet-side bearing arrangement of the turbine shaft is
made inside the exhaust-gas casing construction, and labyrinth
seals and a gland are used for the sealing, barrier air having a
higher pressure than the pressure of the exhaust gas in the
exhaust-gas duct being directed for the shaft sealing into the
gland and then into the exhaust-gas duct, and in which the rotor
cooling air is extracted from a compressor stage and is fed via a
pipeline through the exhaust-gas-side shaft end into the rotor, by
a portion of the rotor cooling-air leakage being diverted after
some of the labyrinth seals and being used as barrier air, and by
ambient air being introduced as cooling air into the bearing space,
which ambient air is uniformly distributed at the periphery via the
gland and is transported to the outside through passages in the
exhaust-gas diffuser.
According to the invention, this is achieved in an apparatus for
carrying out the aforesaid method when the labyrinth seals at the
transition from the rotor cooling-air line to the exhaust-gas-side
end of the cooled rotor are divided and an intermediate tap having
a pipeline, going to the gland, for the barrier air is arranged at
the dividing point, when a further pipeline ending at the gland for
ambient air acting as cooling air is arranged in the bearing space,
the gland being divided into two concentric annular spaces for the
barrier air and for the cooling air, and the bearing space being
fed with cooling air from the annular cooling-air space via bores,
and when the bearing space is subdivided in the top part by means
of a hood and in the bottom part by means of an oil drip plate.
The advantages of the invention can be seen, inter alia, in the
fact that a separate extraction point in the compressor for the
barrier air and therefore a separate barrier-air feed are no longer
necessary, that the leakage-air quantities passing into the bearing
space are minimal, and that uniform cooling at the periphery for
the supporting structure, the bearing and the oil wiper is
achieved, so that the efficiency of the plant is increased.
It is especially convenient when the barrier-air quantity and the
barrier-air pressure are set to an optimum value by changing the
number of labyrinths and the respective gap sizes of the
labyrinths, since the leakage air entering the bearing space can
thereby be kept at a low level and thus no undesirable heating-up
of the bearing space takes place.
Furthermore, it is advantageous when axially running cooling ducts
are arranged between the supporting structure and the insulation in
the inner part of the exhaust-gas casing along the flow ribs,
preferably on either side at the foot of the flow ribs, which
cooling ducts are connected via bores at their turbine-side inlet
part to the annular cooling-air duct of the gland and at their
outlet part to the bearing space, the cooling air from the annular
cooling-air duct flowing through the said ducts. Through the
specific use of the cooling air in the ducts, air is saved and
large heat transfer coefficients are achieved. There are no flow
obstructions and therefore a constant temperature is achieved at
the periphery of the inner casing structure.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the
attendant advantages thereof will be readily obtained as the same
becomes better understood by reference to the following detailed
description when considered in connection with the accompanying
drawings of a single-shaft axial-flow gas turbine, wherein:
FIG. 1 shows a longitudinal section of the exhaust-gas tract of the
gas turbine (overview);
FIG. 2 shows a partial longitudinal section of the bearing area in
the exhaust-gas tract of the gas turbine;
FIG. 3 shows an enlarged detail from FIG. 2 in the area of the
labyrinth/rotor cooling air to rotor;
FIG. 4 shows the dependence of the mass-flow ratios in a divided
labyrinth having an intermediate tap on the ratio of the number of
sealing-strips and the ratio of the labyrinth gap size;
FIG. 5 shows a partial longitudinal section of the bearing
area;
FIG. 6 shows a partial cross-section of FIG. 5 in the area of the
flow ribs .
Only the elements essential for understanding the invention are
shown. Elements of the plant which are not shown are, for example,
the inlet parts of the gas turbine as well as the complete
compressor part. The direction of flow of the working media is
designated by arrows.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, wherein like reference numerals
designate identical or corresponding parts throughout the several
views, the invention is explained in more detail below with
reference to exemplory embodiments and FIGS. 1 to 6, in which FIG.
1 shows as an overview a partial longitudinal section of a
single-shaft, axial-flow gas turbine, of which the exhaust-gas side
and the last stage of the turbine are shown.
For the sake of more clearly recognizing the details, the bearing
area in the exhaust-gas tract is shown in partial longitudinal
section in FIG. 2 and the area of the labyrinth is shown enlarged
in FIG. 3.
According to FIG. 1, the axial-flow gas turbine essentially
consists of the rotor 2 which is equipped with moving blades 1 and
of the blade carrier 4 which is equipped with guide blades 3 and is
hung in the turbine casing 5. Flanged to the turbine casing 5 is
the exhaust-gas casing 6, in which a plurality of flow ribs 12
distributed uniformly over the periphery are arranged. FIG. 2
reveals that the flow ribs 12 encase the supporting ribs 20, which
are surrounded with an insulation 11. The exhaust-gas diffuser 9 is
flanged to the exhaust-gas casing 6.
The outlet-side bearing arrangement of the rotor 2 (bearing housing
14, bearing 15) is arranged inside the exhaust-gas casing
construction. Extending between the bearing housing 14 and the
annular inner part 7 of the exhaust-gas casing 6 is the bearing
space 16, which is sealed off on the turbine side from the
exhaust-gas duct 32 via the gland 18 and from the rotor cooling air
via labyrinth seals 17.
To cool the rotor 2, rotor cooling air R is extracted from the
compressor (not shown here) and, via a pipeline 19, which, coming
from the compressor, leads through one of the passages 8 located at
the end of the exhaust-gas tract and extends in the area of the
extended machine axis up to the exhaust-gas-side shaft end, is fed
through the exhaust-gas-side shaft end into the rotor 2. A leakage
L of this air arises in the gap 21 between the pipeline 19 and the
rotating rotor 2, and all this leakage L, according to the prior
art, escapes into the bearing space 16 and passes into the
surroundings of the bearing 15. This point is normally sealed off
with labyrinth seals 17.
FIG. 3 shows that, according to the invention, the labyrinth 17 is
now subdivided into a labyrinth 17.1 having n1 sealing strips and a
gap width s1 and into a labyrinth 17.2 having n2 sealing strips and
a gap width s2. A pipeline 22 for the barrier air S is arranged
between the two labyrinths 17.1 and 17.2, which pipeline 22 leads
past the bearing housing 14 to the gland 18. Thus a portion of the
rotor cooling-air leakage L is used as barrier air S. So that the
barrier air S has just the requisite pressure, it is extracted
after some of the seals. The leakage-air quantity over the
remaining labyrinths is reduced by this extraction, so that only a
minimum air loss and thus a minimum loss of efficiency occur and
the surroundings of the bearing space are heated up only
slightly.
The invention is of course not restricted to the arrangement of a
single barrier-air line 22. Two or even more pipelines of this type
can be advantageously arranged at any possible points around the
bearing housing.
FIG. 4 shows for one example the dependence of the mass-flow ratios
(mass flow m1 of all the rotor cooling-air leakage L/mass flow m2
of the actual leakage air L2 flowing into the bearing space 16) at
a divided labyrinth on the ratio of the number of sealing strips
(n2/n1) or on the size ratio of the gaps (s1/s2). The mass-flow
ratio m1/m2 increases with an increase in n2/n1 and s1/s2. The
quantity of barrier air S (m1-m2) and its pressure can thus be
changed by changing the number of sealing strips of the labyrinth
seals and by changing the gap sizes.
An essential additional advantage of the solution according to the
invention consists in the fact that no separate barrier-air feed
from the compressor is necessary and that there is also no need for
a separate extraction point for the barrier air S in the
compressor.
So that the bearing space 16 is not heated excessively by the
leakage air and by the heat flow from the exhaust-gas stream A
through the insulation 11 and the supporting structure 10, which
comprises the hub 31 and the supporting ribs 20, it is cooled (see
FIG. 2). The heat entering the bearing space 16 is in the process
transported to the outside through the passages 8 in the
exhaust-gas diffuser 9 by ambient air which is introduced by a fan
23 through a pipe 24 reaching up to the gland 18.
The gland 18 is subdivided into two concentric annular spaces 25,
26, the annular space 25 being used for the barrier air S and the
annular space 26 being used for the bearing-space cooling air K.
The air is uniformly distributed at the periphery by the gland
18.
The bearing space 16 is subdivided into two spaces, in the top part
by means of a hood 27 arranged between bearing housing 14 and
supporting structure 10 and essentially parallel to the supporting
structure 10 and in the bottom part by means of an oil drip plate
28, the requisite cooling-air quantity in the two parts of the
bearing space 16 being determined via bores 29 specifically made in
the gland 18 in the annular cooling-air space 26. Thus the
supporting structure 10 can be cooled specifically and uniformly at
the periphery. At the same time, the surroundings of the bearing
housing 14 and the devices arranged inside the hood 27 are cooled
separately. Furthermore, the hood has the task of preventing the
radiation of heat to devices and bearing housing.
Cold air is likewise specifically introduced near the oil wipers 13
in the top and bottom part from the annular cooling-air space 26.
This ensures that only cold air penetrates into the bearing body
15, in which a slight vacuum is always to prevail.
The advantages of this combined barrier and cooling system consist
in the fact that safe heat dissipation is guaranteed, that uniform
cooling occurs at the periphery for supporting structure, bearing
body and oil wipers, that the cooling-air flows can be specifically
set by selecting the size and number of the openings in the annular
cooling-air space, and that cost savings are possible through the
use of the combined gland.
The invention is of course not restricted to the exemplary
embodiment described above. A further embodiment variant of the
invention is shown in FIG. 5 and FIG. 6. In addition to the
exemplary embodiment described above, cooling ducts 30 are also
arranged here in the supporting structure 10. These cooling ducts
30 are located at the foot of the supporting ribs 20 and are fed
with air from the annular cooling-air space 26 via bores 29. The
cooling ducts 30 are each preferably arranged on either side at the
foot of the supporting ribs 20 and serve to dissipate the heat
coming from the exhaust-gas stream before entering the hub 31 or
the inner space.
With this measure, an exact heat transfer coefficient is achieved
at the foot of the strut, which guarantees accurate heat
dissipation or uniform temperature at all flow ribs 12. Further
advantages can be seen in the fact that, through the specific use
of the cooling air in the cooling ducts, air is saved and large
heat transfer coefficients are achieved. In addition, a uniform
temperature is achieved at the periphery of the inner casing
structure, since the air flows in ducts and consequently there are
no flow obstructions.
Obviously, numerous modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *